A slightly modified form of the branched pore model of Peel, Benedek and Crowe was successfully applied to describe the batch sorption kinetics of three metal ions-cadmium, copper and zinc-on bone char. In comparison with an analytical film-surface solution, the additional parameters of the branched pore model were observed to produce a significant improvement in correlating the experimental results. The ranges of the values of the model parameters derived were deemed reasonable and the branched pore sorption capacities of two of the three metal ions were comparable (ca 0.16 mmol g(-1)). Given that the surface diffusivities of the metal ions were observed to vary with averaged surface loading, a number of correlations were examined for their accuracy in describing this behaviour. The exponential expression of Neretnieks resulted in the smallest total error when the data for all three metal ions were considered together. (c) 2005 Society of Chemical Industry.